1. Field of the Invention
The present invention generally relates to eccentricity correction methods, signal processing circuits, magnetic storage apparatuses and perpendicular magnetic recording media, and more particularly to an eccentricity correction method for correcting eccentricity by reproducing an eccentricity correction data that is recorded by a recoding head from a perpendicular magnetic recording medium that is prerecorded with servo information by a magnetic transfer, a signal processing circuit and a magnetic storage apparatus that employ such an eccentricity correction method, and a perpendicular magnetic recording medium that is recorded with an eccentricity correction data in an easily reproducible manner.
2. Description of the Related Art
A magnetic disk is prerecorded with servo information for controlling a position of a head with respect to the magnetic disk. The servo information may be recorded by a recording head or, by a magnetic transfer that applies magnetization in an in-plane direction or a perpendicular direction with respect to the magnetic disk. The magnetic transfer itself is known, as may be seen from a Japanese Laid-Open Patent Application No. 2004-342297.
After the magnetic disk that is prerecorded with the servo information is assembled into a magnetic disk drive, an eccentricity correction data for correcting eccentricity of the magnetic disk is recorded on the magnetic disk by a recording head. The eccentricity correction is carried out in real-time by reproducing the eccentricity correction data from the magnetic disk by a reproducing head.
FIG. 1 is a system block diagram showing an important part of a conventional magnetic disk drive. A magnetic disk drive 1 shown in FIG. 1 includes a preamplifier part 2, a read and write part 3, a hard disk controller (HDD) 4, and a servo controller (SVC) 5. The preamplifier part 2 includes an amplifier 21 and a driver 22. The read and write part 3 includes a synchronizing circuit 31, a prefilter 32, a switching circuit 33, a data demodulating circuit 34, a servo demodulating circuit 35, a post processor 36, a recording compensation circuit 37, and a driver 38.
FIG. 2 is a diagram showing a format on a conventional perpendicular magnetic disk. The perpendicular magnetic disk is provided with a servo region in which servo information is prerecorded by a recording head. Data are recorded in a data region which follows the servo region. A preamble #1, servo mark and address, and servo burst are prerecorded in the servo region. After the perpendicular magnetic disk is assembled into the magnetic disk drive 1, an eccentricity correction data is recorded in the servo region by the recording head subsequent to the servo burst. At the time of a recording, the data is recorded subsequent to a preamble #2. At the time of a reproduction, the recorded data is reproduced from the data region. The data that are reproduced and recorded with respect to the data region are shown as R/W (read/write) data in FIG. 2.
Information reproduced from the perpendicular magnetic disk (not shown) by the reproducing head (not shown) is supplied to the data demodulating circuit 34 and the servo demodulating circuit 35 via the amplifier 21, the synchronizing circuit 31 and the prefilter 32. The synchronizing circuit 31 generates a clock and a servo mark from the reproduced information, and supplies the clock and the servo mark to the switching circuit 33. The switching circuit 33 controls switching of the demodulating circuits 34 and 35 based on the clock and the servo mark, so that the output of the prefilter 32 is demodulated by the servo demodulating circuit 35 while reproducing the information from the servo region and the output of the prefilter 32 is demodulated by the data demodulating circuit 34 while reproducing the information from the data region. Output reproduced data from the data demodulating circuit 34 are supplied to the HDC 4, and output reproduced servo information from the servo demodulating circuit 35 is supplied to the SVC 5. The reproduced data are supplied to other parts within the magnetic disk drive 1 or, output outside the magnetic disk drive 1, via the HDC 4. The reproduced servo information is used for various kinds of control operations of the magnetic disk drive 1 in the SVC 5.
At the time of the recording, the recording data are supplied to the recording head (not shown) via the HDC 4, the post processor 36, the recording compensation circuit 37 and the drivers 38 and 22. Hence the recording head records the recording data within the data region on the perpendicular magnetic disk subsequent to the preamble #2.
According to the format shown in FIG. 2, both the information within the servo region and the information within the data region that are reproduced by the reproducing head are reproduced in the form of a rectangular wave. Hence, the prefilter 32 has a differentiating characteristic.
However, the method of recording the servo information on the magnetic disk by the magnetic transfer is more efficient that the method of recording the servo information by the recording head, in that the servo information can be recorded simultaneously, that is, in a batch. In addition, in the case of the magnetic transfer that applies the magnetization in the in-plane direction with respect to the perpendicular magnetic disk, it is further desirable in that the signal-to-noise ratio (SNR) improves. FIG. 3 is a diagram showing a format on a perpendicular magnetic disk that is recorded with the servo information by the magnetic transfer which applies the magnetization in the in-plane direction with respect to the perpendicular magnetic disk, and is also recorded with the eccentricity correction data by the recording head.
But in the case of the perpendicular magnetic disk that is recorded with the servo information by the magnetic transfer which applies the magnetization in the in-plane direction with respect to the perpendicular magnetic disk and is recorded with the eccentricity correction data by the recording head, the preamble #1, the servo mark and address, and the servo burst that are reproduced by the reproducing head are reproduced in the form of differentiated waveforms and cannot be subjected to the same process as the eccentricity correction data within the servo region and the information within the data region that are reproduced in the form of rectangular waveforms. In other words, if the prefilter 32 has a differentiating characteristic, this prefilter 32 will not be suited for processing the preamble #1, the servo mark and address, and the servo burst within the servo region that are reproduced in the form of differentiated waveforms, and cannot carry out a suitable prefiltering with respect to the servo information that is to be supplied to the servo demodulating circuit 35. On the other hand if the prefilter 32 has a non-differentiating characteristic, this prefilter 32 will not be suited for processing the eccentricity correction data within the servo region and the information within the data region that are reproduced in the form of rectangular waveforms, and cannot carry out a suitable prefiltering with respect to the eccentricity correction data to be supplied to the servo demodulating circuit 35 and the data to be supplied to the data demodulating circuit 34.
For this reason, in the case of the perpendicular magnetic recording medium that is prerecorded with the servo information by the magnetic transfer which applies the magnetization in the in-plane direction with respect to the perpendicular magnetic recording medium, there was a problem in that the eccentricity correction cannot be made by reproducing the eccentricity correction data that has been recorded by the recording head.